1. Field of the Invention
The present invention is directed to an optical switch and, more particularly, to an optical switch, which steers an optical beam from an input port to an output port without intermediate conversion to an electrical signal, by using phase changing phase spatial light modulators comprising interferometers (IPSLMs).
2. Description of the Related Art
Fiber optic infrastructures are being implemented for many communication networks, including packet switched networks such as the Internet. In these communication networks, optical signals imposed on light beams are transmitted along optical fibers. At network nodes, the optical signals arrive on input optical fibers and leave on output optical fibers. Routing of a signal between input and output fibers at these network nodes is generally performed by conversion of the light signal from an input fiber to an intermediate electrical form, and then switching is performed on the electrical signal which is then converted back into a light signal in the output fiber. These conversions are slow and expensive and constitute a major cost element of an optical fiber network.
An optical switch is needed which directly switches a beam of light between input and output fibers quickly and without conversion to an intermediate electrical signal.
One technique that has been developed for direct switching of an optical signal between input and output fibers employs rotating mirrors to direct a reflected light beam. However, because of the mass of the mirrors involved, a rotating mirror is not fast enough for most packet switching networks.
U.S. Pat. No. 6,430,328, which is herein incorporated by reference in its entirety, uses optical phase changing SLMs (PSLMs) beam reflectors in which optical switching is performed by changing the relative phase of the individual portions of the cross section of a wave front of a light beam. The phase change, which is produced by the movement of an array of small phase shifting elements, is proportional to their motion. The individual portions of the wave front are advanced twice the distance that each respective phase shifting elements is moved, and it is advanced in essentially the direction of motion of the phase shifting elements. An array of such phase changing elements placed in the beam can cause the phase of the beam to increase linearly across the individual portions of the cross section of the wave front of the beam, thus causing a light beam deflection. Because the phase shifting elements are small relative to a rotating mirror used in other switches, they have less mass and can be moved from one switch position to another much faster. In addition, the total motion of the phase shifting elements need not exceed one half wavelength of the light being switched, which is less than the motion of a substantial portion of a rotating mirror for an equivalent beam deflection. Thus the PSLM beam reflector can switch an optical beam into a desired direction much faster than an equivalent rotating mirror device. Because the throughput of a typical network can be limited by switching speed within the network, what is needed is an optical switch, which will switch from an input fiber to an output fiber faster. This can be done by decreasing the mass of phase shifting elements and by decreasing or substantially eliminating their movement.
It is an aspect of the present invention to perform optical switching for an optical network by interferometrically controlling the relative phase of the individual portions of the cross section of the wave front to steer a beam.
It is also an aspect of the present invention to provide an optical switching device to perform optical switching for an optical network by interferometrically controlling the relative phase of individual portions of the cross section of a wave front to steer a beam.
It is another aspect of the present invention to use interferometric phase spatial light modulators (IPSLMs) that include an array of phase shifting elements in such a manner that each of the phase shifting elements has a stationary reflective surface and a movable reflective surface which moves a maximum distance substantially less than one half of the wavelength of the light beam.
It is a further aspect of the present invention to use IPSLMs that use optical wave path changes to perform optical switching for an optical network by changing the relative phase of the individual portions of the cross section of the wave front of a beam.
It is another aspect of the present invention to use IPSLMs that use a material, which changes refractivity with applied electrical potential, to perform optical switching for an optical network by changing the relative phase of the individual portions of the cross section of the wave front of a beam.
It is also an aspect of the present invention to use IPSLMs that have an array of phase shifting elements comprised of interferometers to change the relative phase of individual portions of the cross section of the wave front of a beam to steer the beam in a desired direction.
It is another aspect of the present invention to use IPSLMs to perform optical switching of one optical fiber to another optical fiber in less than about 100 nanoseconds for an optical network by changing the relative phase of the individual portions of the cross section of the wave front of a beam.
It is an additional aspect of the present invention to use IPSLMs to perform optical switching of one optical fiber to another optical fiber in less than about 10 nanoseconds for an optical network by changing the relative phase of the individual portions of the cross section of the wave front of a beam.
It is an aspect of the present invention to provide either IPSLMs or PSLMs that include an array of phase shifting elements and a prism or other spectral dispersing element in a Litrow spectroscope configuration to deflect and also separate individual wavelengths of a wavelength division multiplexed (WDM) light signal.
It is also an aspect of the present invention to provide either IPSLMs or PSLMs that include an array of phase shifting elements to produce a wave front desired phase distribution by changing the relative phase of the individual portions of the cross section of the wave front of a beam.
The above objects can be attained by a system that includes one or more light modulators, IPSLMs or PSLMs, as optical reflectors in an optical switching system. One or more input light beams are deflected by one or more input optical reflectors. One or more output optical reflectors can further deflect the beam. Each reflector changes the direction of the light beam by changing the phase of the wave front segments by changing the optical wave path length of phase shifting elements relative to each other. The IPSLMs are comprised of interferometers and change the relative phase of portions of a beam wave front to steer the beam in a desired direction.
These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.